1. Field of the Invention
The present invention relates to input devices such as a mouse, a touch panel, and a pen input device and, more particularly, to a coordinate input device which permits a user to perform a pointing operation on both the display screen of a monitor and the top surface of a desk.
2. Description of the Related Art
A conventional optical digitizer includes a pair of line cameras mounted on the upper left and the upper right positions of a display screen of a monitor, and processes video signals picked up by the cameras which capture the image of the surface along the display screen. The digitizer thus detects the position of a user's finger or a pen. An outline frame is arranged on the periphery of the display screen so that no unwanted light is incident on the cameras.
When such a technique is applied on the monitor of a personal computer for use on the desk top, the display screen is operated using a finger or a pen like a touch panel. This arrangement permits the user to operate the personal computer in an intuitive fashion.
The display screen of the monitor is typically placed to be vertical to the desk top. Inputting characters and drawings through hand-writing forces the user to be in an uncomfortable position often for a long period of time, thereby fatiguing the user.
When touch input is performed on the display screen, the user's finger or the pan, if placed in the vicinity of the display screen, triggers an unintended input operation. This is because the system detects a touch input at the moment the pen enters the outline frame having a certain width in the image of the camera having the field of view covering the outline frame.